1. Field of the Invention
The present invention relates to orthotic devices utilized to limit the movement of a lower limb. More particularly, the present invention relates to an ankle-foot orthosis for stabilizing and controlling motion of the ankle and foot.
2. Description of the Related Art
An ankle-foot orthosis is a medical device used to support and align the ankle and foot by suppressing spastic and overpowering ankle and foot muscles, assisting weak and paralyzed muscles of the ankle and foot, and preventing or correcting ankle and foot deformities.
An ankle-foot orthosis is particularly useful in assisting the functions of the ankle and foot when a person has a gait condition commonly known as “drop foot.” Drop foot is a neuro-muscular condition resulting in the inability of a person to sufficiently lift one of their feet during a walking stride. Drop foot may result from a cerebrovascular accident, spinal cord injury, hereditary and sensory neuropathies, neuromuscular disease or any damage to the muscle and nerves required to activate the muscle of the neuromuscular system related to the foot.
There are two common complications from drop foot. First, the individual cannot control the falling of their foot after striking their heel. Consequently, the foot will slap the ground on every step, which is commonly referred to as slap foot. This is typically due to the impairment of a patient's dorsiflexor muscles which are located below the knee on the front of the leg and used to lift the foot from a position substantially aligned with the lower leg to a position substantially perpendicular to the lower leg known as dorsiflexion. Impairment of the dorsiflexor muscles thus results in excessive plantar flexion which is the action of extending the foot from a position substantially perpendicular to the lower leg to a position substantially parallel to the lower leg. The second complication is the inability to clear the toe during the swing phase of a gait cycle. This causes the person to drag their toe on the ground throughout the swing phase. Hence, an ankle-foot orthosis can be prescribed to compensate for the weakness of the dorsiflexors by resisting plantar flexion at the heel strike and swing phase during a gait cycle.
Typically, an individual with drop foot may have little or no function in their anterior tibialis. The anterior tibialis originates at the lateral condyle of the tibia and extends along the lateral side of the tibia to cross the tibia near a distal portion thereof over to the medial side of the ankle to connect with the first metatarsal bone and medial cuneiform bone. Proper function of the anterior tibialis permits dorsiflexion and inverts the foot at the ankle in a supinated position. The anterior tibialis also supports the medial arch of the foot due to its connection to the medial cuneiform bone.
Individuals who have lost function of the anterior tibialis tend to pronate during a stance phase of a gait cycle, and supinate the foot during a swing phase of a gait cycle. Furthermore, due to impairment of the anterior tibialis, in particular at the medial arch of the foot, the ankle is typically everted and pronated.
Over the years, efforts have been made to provide ankle-foot orthotic devices to correct drop foot and enable a patient to walk and function in a relatively normal manner. One type of prior art ankle-foot orthosis comprises a dorsal splint of metal or plastic that extends behind the Achilles tendon and merges with a foot plate spanning the sole of the foot. This ankle-foot orthosis has at least one strap which extends around the lower leg at a location below the knee. This ankle-foot orthosis is disadvantageous in that the orthosis extends along the dorsal portion of the leg and affects the joints unfavorably to produce a very stiff gait. Another disadvantage to this orthosis is that the calf and Achilles tendon are subjected to heavy stresses which may cause pain and discomfort to the patient wearing the orthosis. Yet further, this orthosis has an undesirable effect on a patient's leg during a gait cycle since the orthosis is solely positioned on the back of the heel and therefore does not provide a smooth heel strike.
Another type of prior art ankle-foot orthosis is produced by Otto Bock and sold under the trade name “Walk On.” This ankle-foot orthosis is fabricated from carbon fiber reinforced material to provide moderate resistance to plantarflexion and dorsiflexion as well as some coronal plane control. The construction of this orthosis includes a footplate connecting to a calf band via a small carbon fiber spring that extends around the medial malleolus and extends up the posterior calf region, and further includes a strap that secures the orthosis to the lower leg. The foot plate provides compression at heel strike, energy return from a mid-stance to toe off, easy toe rollover by including increased stiffness from heel strike to midstance and decreased stiffness from midstance. This design is less conspicuous when worn, since it extends around the medial malleoulus and the carbon fiber reinforced material is wear resistant. Furthermore, this design has the advantage over conventional plastic posterior designs in that it extends over the medial side of the foot, and therefore provides the orthosis with a heel part and a toe part that contribute to a smoother heelstrike. Contrariwise, a disadvantage to this orthosis is that it permits a significant degree of plantar flexion since it lacks proper anterior support and only reinforces the posterior of the ankle and foot. Moreover, this design does not provide any lateral support, and therefore, unless people wear high and strong shoes, inversion of the foot is not prevented.
In another variation of an ankle-foot orthosis, U.S. Pat. No. 5,897,515 discloses an ankle-foot orthosis that includes a frame of flexible material that extends over the anterior portion of the lower leg and the lateral ankle, and further extends beneath a portion of the sole of the foot to connect to a foot plate. This orthosis requires at least one substantially inflexible reinforcement element extending over a narrow part of the anterior portion of the frame. In practice, it has been found that the anterior shell covering the lower leg can cause a patient discomfort due to the amount of area covered along the anterior portion of the leg, thereby resulting in an excessively sweaty area and an undesirable amount of pressure exerted on the tibia region when walking. Furthermore, this orthosis has been found to suffer from breakage problems particularly in a region where the orthosis extends over the lateral ankle and connects to the foot plate.
In an orthosis that includes a strut that extends over a lateral portion of the tibia, as in the orthosis of U.S. Pat. No. 5,897,515, a patient may have adequate support during the swing phase of their gait, but will not have sufficient support to prevent eversion of the foot during the stance phase of their gait. The lack of support during the stance phase is due in part to the lack of support to the medial arch of the foot and the overall failure of the lateral strut to support the length of the anterior tibialis. While many conventional ankle-foot orthoses with a laterally extending strut may provide a patient with more control for dorsiflexion and inhibit excessive plantarflexion, it has thus been found that these orthoses fail to provide adequate support to the medial arch of the foot. As a result, patients that wear these conventional orthoses do not have sufficient force to keep their foot from pronating since their ability to invert the foot has not been increased. Moreover, orthoses with only lateral struts do not provide sufficient valgus control, thereby insufficiently stabilizing an ankle and failing to enable adequate ankle articulation.
With all of the aforementioned orthoses, each fail in part to adequately provide sufficient medial support during a stance phase of a patient's gait and sufficient lateral support during a swing phase of a patient's gait.
Accordingly, it is readily apparent that there is a need for an ankle-foot orthosis that provides support for both the medial and lateral ankle portions of a patient, dynamic dorsiflexion and plantar flexion support, a foot plate permitting easy toe rollover, and a dynamic design which is more durable and less prone to material failure through normal use.